Bullet diameter was typically .512" (13.004 mm) diameter. However, older black powder rounds with lead bullets are frequently loaded with a variation of bullet diameters based on which particular diameter shoots best in that particular gun. The type of rifling (grooves), bullet composition (lead/tin/alloy), etc. affect how well a particular diameter bullet will shoot.

Bullet weights ranged from 425 grains (27.54 g) at approximately 1400 ft/sec (426.72 m/s) to a much heavier and more powerful 550 grains (35.64 g) at approximately 1275 ft/sec (388.62 m/s).

The .50-90 was created specifically with buffalo in mind. At the time, the killing power of a cartridge could only really be altered by making a heavier bullet or increasing the powder charge. The wide variety of specialty bullets and powders was not available. The buffalo is an extremely large animal and difficult to take down reliably, thus the need for a large diameter cartridge, capable of carrying a heavier bullet, more powder, and a greater cross-section on the bullet, creating a larger hole. [2]

Today the round is almost obsolete. Ammunition is not produced by any major manufacturer. Rifles are only produced on an infrequent basis by a few companies such as Shiloh, Uberti, and C&S. The rifles are typically used for buffalo hunting and reenactments. Occasionally they are used for vintage competitions, but the heavy bullet and powder charge produce more recoil than other old-time cartridges such as the .45-70, and so are used less frequently.